1. Field of the Invention
The present invention relates to an image sensor used for the image input section of a facsimile system and the like.
2. Description of the Related Art
FIG. 12 is a side view of the conventional image sensor disclosed in, for example, the official gazette of Japanese Unexamined Patent Publication No. 6-169370. FIG. 13 is a sectional view of the image sensor in FIG. 12, taken along the line XIII-XIII in FIG. 12. In FIGS. 12 and 13, a frame 7 is formed into an almost rectangular-parallelepiped frame having a length almost equal to the width of a manuscript 100 to be read, which has a first plane 7a, a second plane 7b facing the first plane 7a, and two sides 7c and 7d connecting the first plane 7a and the second plane 7b and whose inside is almost hollow. The hollow portion has an aperture on the first plane 7a and the second plane 7b and it is formed over the almost overall length of the frame 7 long the longitudinal direction. In the hollow portion, a protrusion 7e is formed over the almost overall length along the longitudinal direction from the back of the side 7d toward the inside of the frame 7. The protrusion 7e divides the hollow portion into two hollow portions such as a first hollow portion 7f and a second hollow portion 7g.
The protrusion 7e supports an erect-1.times.magnification-image-forming rod lens array 4 extending along the longitudinal direction of the frame 7 in the hollow portion. The rod lens array 4 is extended over the almost overall length of the frame and constituted by linearly connecting a plurality of rod lenses. In FIG. 13, though the protrusion 7e seems to be divided at a portion for supporting the rod lens array 4, it is integrally connected to the both ends of the frame 7.
A rectangular flat glass plate 6 extending in the longitudinal direction of the frame 7 is secured to the first plane 7a of the frame 7 so as to cover the aperture. Moreover, a rectangular flat light-receiving-element mounting substrate 2 extending in the longitudinal direction is set to the second plane 7b so as to cover the aperture. Reference planes 7h and 7i are formed on the margin of the aperture formed on the second plane 7b along the longitudinal direction of the frame 7. The light-receiving-element mounting substrate 2 is positioned because the reference planes 7h and 7i are pressed against the substrate 2 and secured by a securing hardware 13. The securing hardware 13 is made of an elastic metal and has an U-shaped cross section, on whose both ends a pawl 13a is formed. Moreover, a groove 7j is formed on the sides 7c and 7d of the frame 7 along the longitudinal direction so as to engage with the pawl 13a respectively. The securing hardware 13 is set in places at almost equal intervals along the longitudinal direction of the frame 7 to secure the light-receiving-element mounting substrate 2.
A plurality of light-emitting diodes 3 are linearly arranged on the mounting plane facing the hollow portion 7f of the light-receiving-element mounting substrate 2 along the longitudinal direction of the frame 7 to constitute a line light source.
Moreover, a plurality of sensor ICs 5 are linearly arranged on the mounting plane facing the hollow portion 7g of the light-receiving-element mounting substrate 2 long the longitudinal direction of the frame 7 at a pitch of several millimeters. The sensor ICs 5 are arranged so as to face the rod lens array 4.
An image sensor thus constituted is used for, for example, an apparatus such as a facsimile system and the manuscript 100 to be read moves while contacting the glass plate 6. The light emitted from a plurality of light-emitting diodes 3 serving as a line light source passes through the glass plate 6 to illuminate the manuscript 100.
The illumination light reflects in accordance with the light-and-shade information of an image drawn on the manuscript 100 and passes through rod lenses of the rod lens array 4, and it is condensed to the sensor ICs 5. A plurality of sensor ICs 5 accumulate electric charges in accordance with the intensity of reflected light and the accumulated electric charges are output through the light-receiving-element mounting substrate 2.
The conventional image sensor is constituted as described above and the securing hardware 13 is provided in places along the longitudinal direction of the frame 7. Therefore, the light-receiving-element mounting substrate 2 at a portion for which the securing hardware 13 is not provided is separated and lifted from the reference planes 7h and 7i. Thus, the optical positional relation between the sensor ICs 5 on one hand and the manuscript 100 or the rod lens array 4 on the other collapses and therefore, the focus is deviated and the resolution is deteriorated as an image sensor.
Moreover, fluctuation occurs in the pressure for the securing hardware 13 to press the light-receiving-element mounting substrate 2 depending on the range of the dimensional tolerance of the thickness of the light-receiving-element mounting substrate 2, that of the securing hardware 13, or that of the groove 7j and the light-receiving-element mounting substrate 2 is lifted from the reference planes 7h and 7i and the resolution is deteriorated when the pressure is too low. Moreover, when the pressure is too high, the light-receiving-element mounting substrate 2 is deformed and thereby, the sensor ICs 5 mounted on the substrate 2 may be removed.